Transistor oscillators



July 17, 1962 E. M. JONES TRANSISTOR OSCILLATORS Filed Dec. 51, 1956 2Sheets-Sheet 1 D.6.50URCE REPET/T/VE PULSE saunas MASTER 05C PULSE fSOURCE a pup r25 BASE W01. r405 Wi F/G. 5

F/6f6 e a H b m ,NVENTOR 0 Edward M. Jones Z BY H67 AGENT Unite Statesatent I 3,045,192 Patented July 17, 1962 free 3,045,192 TRANSISTOROSCELATORS Edward M. Jones, Cincinnati, Ohio, assignor to The BaldwinPiano Company, Cincinnati, Ohio, a corporation of Ohio Filed Dec. 31,1956, Ser. No. 631,681 1 Claim. (Cl. 331 111) This invention relates torelaxation oscillators employing semi-conductive devices, such astransistors, and in particular relates to systems for locking thefrequencies of a plurality of such oscillators in integralrelationships. Such systems of cascaded oscillators have heretofore beenproposed for counting, scaling and frequency division purposes. Apreferred embodiment of my invention is particularly useful andadvantageous in providing octavelyrelated, complex oscillations inelectronic musical instruments of the type wherein twelve cascadedgenerators are used, each one supplying all the octavely-related notesof the same nomenclature.

A principal object of my invention is to provide a transistor frequencydivider circuit having a common base connection to all the transistorssuch as will permit the use of multiple transistor units having severalpairs of emitter and collector electrodes contacting the same crystal orhaving several crystals mounted on a common heatdissipating base.

An important object of my invention is toprovid'e a divider circuit forsemi-conductive devices in which synchronizing pulses of stableamplitude are produced.

Another object, which is particularly important in electronicmusicalinstrument usage, is to provide a divider circuit in which thesemi-conductive devices operate at low duty cycle so as to reduce theamount of subharmonic modulation fed back from one stage to a previousstage.

A further object is to provide a frequency divider cir-' cuit,particularly for electronic musical instruments, wherein the DCcomponent is eliminated from the output oscillations of the circuit.

A further object of my invention is to provide an inexpensive and simplerelaxation oscillator circuit having a minimum number of electricalcomponents.

These and other objects of the invention which will be set forthhereinafter, or will be apparent to one skilled in the art upon readingthese specifications, are accomplished by those constructions andarrangements of parts of which certain exemplary embodiments will now bedescribed. Reference is made to the accompanying drawings wherein:

FIGURE 1 is a circuit diagram of a frequency divider circuit inaccordance with the present invention;

FIGURE 2 is a circuit diagram of a modification of the system of FIGURE1;

FIGURE 3 is a circuit diagram illustrating how a pair of complementaryjunction transistors may be connected for use in the practice of myinvention;

FIGURE 4 illustrates how connections may be made to a particular type ofsemi-conductive device for use with my invention;

FIGURE 5 illustrates another embodiment of a semiconductive device whichmay be employed in the practice of my invention;

FIGURE 6 illustrates the manner in which connections may be made tostill another type of semi-conductive device for use with my invention;I

FIGURE 7 illustrates certain wave forms, useful in explaining theoperation of the system;

FIGURE 8 is aview in transverse section taken through FIGURE 9, andenlarged to indicate details of construction; and

FIGURE 9 is a functional diagram of a system according to the invention,utilizing one specific but exemplary form of common base multiplecontact sets transistor.

Referring now more particularly to the accompanying drawings, FIGURE 1illustrates a circuit diagram of two similar stages 1 and 2 of acascaded frequency divider. A repetitive pulse source 5, of positivelygoing pulses, may be a master oscillator of any suitabletype, producingshort duration pulses periodically. One example of a suitable source isdisclosed in a copending patent application in the name of Jones andWinder, filed December 31, 1956, Serial No. 631,682, now Patent No.2,902,655, and entitled Transistor Oscillators, another example beingdisclosed in the United States patent to Jones, No. 2,555,038. Oneterminal of the source 5 may be connected to a common return path 7,while the other terminal supplies periodic pulses through a resistor R1to a common junction point 9, to which is also connected one end of aresistor R2, the other end of which is connected to a common path 11'from one terminal of a source 13 of direct current. The other terminalof the DC. source 13 may be connected to the common return path 7 Thecommon path 11 is maintained at approximately 20 v. negative withrespect to common return path 7, by source 13.

A capacitor C1 and a resistor R3 may be connected .in series between thejunction point 9 and the common return path 7. The common juncture 15between the capacitor C1 and the resistor R3 has a connection to anemitter terminal a of a semi-conductive device, T1, which may be, forexample, a point-contact transistor, the terminal c being the baseconnection to a block of semiconductor material, and the terminal bidentifying the socalled collector electrode. In accordance with theteachings of my invention the base connection c is made directly to thecommon path 7, while the collector electrode is connected through aresistor R4 to the common junction point 9. The series of elements asdescribed constitutes stage 1 of the frequency divider and, as will beexplained hereinafter, there will occur at the junction point 17 aseries of periodic pulses, the repetition frequency of which will be anintegral submultiple of the frequency supplied to the stage 1 from therepetitive pulse source 5. A saw-tooth wave-form at the dividedfrequency will also appear across the resistor R3, which, as will alsobe explained hereinafter, may be used as a signal take-oil point, ifdesired.

Stage 2 of the frequency divider of FIGURE 1 is similar to stage 1except that the capacitor C2. will be selected of a higher capacity thanthe corresponding capacitor C1 of stage 1, so that the time constant ofthe stage will be lower than that of the preceding stage by' an amountwhich is of the order of the dividing ratio be tween adjacent stages.Corresponding resistors and junction points are similarly designated inthe two stages, except for the prime indication. For example, Rl'ofstage 2 corresponds to R1 of stage 1. i T

The operation of the stage 1 is in certain respects simi lar to that ofother transistor relaxation oscillator circuits currently known in theart (see RCA Review, March 1949, pp. 14-16, and December 1949, pp.463-471), one principal improvement residing in the employment of thecollector resistance R4, which is made unusually low for the purpose ofdischarging the capacitor C1 in a very short time, so that train E, ofvery narrow pulses p1, p2 (see FIGURE 7a) is produced. at the collectorb. These voltage pulses have amplitudes nearly equal to thesupplyvoltage E of the source 13 and is transferred to the second stagethrough the resistor R1. If the transistor T2 is out off, the triggerpulses appearing at circuit points 9 and 15' are very nearly equal tothe value expected from the voltage dividing effect If the trigger pulsebrings the emitter voltage 123 (see FIGURE 7b) of transistor T2 positivewith respect to the base voltage, the collector current will startincreasing, causing an increased voltage rise in R2, which istransmitted through capacitor C2 to further increase emitter voltage 23.The emitter now has a low impedance, and a current gain of only slightlygreater than one is required in the transistor to cause a rapidregenerative increase in emitter and collector current. The collectorcurrent then immediately increases to a value which provides suf'ricientpotential across resistance R4 to lower the magnitude of negativecollector potential (see FIGURE 70) sufficiently to bring the currentgain back down to unity. The resistor R4 is chosen to limit collectorcurrent, assuring that the collector current is safely under theallowable peak current for the point-contact transistor employed. Sincethe emitter voltage e3 never goes very positive, the potential e2(FIGURE 7d) is initially quite negative due to the charge on thecapacitor C2. However, due to the relatively heavy emitter current, thecapacitor C2 is quickly discharged so that e2 rises quickly (point B ofFIGURE 7d) toward ground potential. During this discharge, the collectorvoltage 64 remains approximately constant (see FIGURE 70) at severalvolts negative, but the current in R2 becomes appreciable, causingemitter current to drop considerably below the magnitude of collectorcurrent.

The capacitor C2 is eventually discharged to a point where the emittercurrent is sufficiently low relative to the collector current that thecollector voltage, e4, begins to become more negative. This implies anegative impedance relationship between collector voltage and collectorcurrent. The emitter voltage e3 is still changing very slowly, so theemitter impedance is very small and the capacitor C2 prevents any suddenchange in e2. When the magnitude of this negative impedance at thecollector exceeds the value of R4, the decrease in voltage drops acrossR4 fails to keep up with the increase in magnitude of negative collectorVoltage e4 demanded by the transistor to maintain a given decrease inmagnitudes of collector and emitter current. The transistor T2 thusfinds itself in a situation such that, at a given collector voltage, itscollector current has a greater magnitude than the emitter current wouldnormally allow. The

- collector current therefore rapidly decreases, making the collectormore negative, but the emitter current decreases also, making an evengreater discrepancy between the actual collector currents and thecollector current than would be predicted from the values of emittercurrent and collector voltage alone.

When the magnitude of the collector current has decreased sufiiciently,the emitter current becomes negative and the emitter voltage e3 rapidlygoes negative. Equilibrium is reached when the emitter voltage magnitudeequals the magnitude of the supply voltage minus the voltage drop inresistance R2 due to the residual emitter and collector currents andminus the charge on the capacitor C2. This charge on the capacitor isessentially the same as occurs when negative impedance appears at thecollector, since the entire process involved in the transistor reachingequilibrium in a cut-off condition requires only a fraction of amicrosecond, compared with the 2 to 50 microseconds period during whichheavy emitter current was discharging the capacitor C2.

After the transistor T2 has been cut off, the capacitor C2 charges at amore leisurely rate (see point A of FIG- URE 7b) through resistor R3 andthe back-resistance of the emitter. To render the charging rate lessdependent upon the characteristics of the transistor T2, it is desirableto make resistor R3 several times less than the emitter back resistance.The time constant of this circuit is arranged to be such that when thefirst trigger pulse p1 from stage 1 arrives, the emitter voltage e3 isstill too of the resistors R1 and R2.

negative for the trigger pulse to have any effect, but when the secondtrigger pulse p2 arrives, the emitter is driven positive enough for theregenerative action in the tran sistor hereinabove described to takeplace. The stage thus acts as a frequency divider, having a divisionfactor 2.

Since a saw-tooth signal having the same wave shape as the emittervoltage e3 appears across the resistor R3, a portion of the resistor R3may be used as a signal take-oil point.

The transistor circuit may have such characteristics, with such suitableselection of components as will be suggested hereinafter in connectionwith the embodiment of FIGURE 2, that in the absence of trigger pulses,it will not function as a self-sustaining relaxation oscillator. This isbecause, when the emitter current is zero, which is approximately thefinal condition towards which the capacitor C2 discharges the impedanceof the emitter of the transistor is still fairly high and comparable toR2, and therefore if the transistor has some current gain, asufiiciently large proportion of the collector current increment isshunted through R2 that regenerative feedback to the emitter cannotoccur. This implies that the transistor will fire only upon applicationof a trigger pulse. It is not necessary to the operation of the system,however, that a stage be inoperative until triggered, so long as thefrequency of oscillation is lower than the trigger frequency. Under thelatter circumstances, the trigger will cause the stage to besynchronized at the divided frequency.

Reference is now made to FIGURE 2, wherein is illustrated an embodimentof my invention preferred for use as a tone-wave generator in anelectronic musical instrument. The master oscillator 19 is preferably atransistorized oscillator having a pulse-shape output, as disclosed inthe above-mentioned copending application of Jones and Winder, with aconnection to a common return. The output of the oscillator 19 is passedthrough a resistor R5 to a junction point 21. From this junction pointproceed connections to a resistor R7 and directly to the collectorelectrode 12 of a semi-conductive device T3, which may be, as pointedout in connection with the embodiment of my invention illustrated inFIGURE 1 of the drawings, a point-contact transistor or other suitablesemi-conductive device, or combination of such devices, variousembodiments of which are illustrated in FIG- URES 3, 4, 5 and 6. Thevarious other connections to the semi-conductive device T3 are made asshown, resistors R5, R6 and R7 serving purposes similar to those ofresistors R1, R2, and R4, respectively, of FIGURE 1. The capacitor C3 ofFIGURE 2 is similar in function to capacitor C1 of FIGURE 1, while aresistive divider comprising resistors R8 and R9 has been substitutedfor the resistor R3 of FIGURE 1. The common junction between resistor R8and R9 may be utilized as a signal take-off point to signal outputterminals 23 and 25, the latter being connected to a common returnpoint. A source of negative DC. potential may be connected to theterminal 27, while a source of low positive potential E1 may beconnected to the terminal 29, the point of zero potential at the sourcebeing connected to a common return path, indicated as a groundconnection. A second stage may be connected to the first stage Withcorresponding resistors in the several stages identified bycorresponding reference symbols, prime designations indicating resistorsof the second stage. The capacitor C4 will have a value substantiallydifferent from the capacitor of C3, depending upon the dividing ratio ofthe circuit, but other circuit components may be identical in theseveral stages.

The operation of the circuit of FIGURE 2 is similar to that of FIGURE 1,the differences being (1) that the resistor R5 is connected to thecollector end of the resistor R7 rather than to the emitter end, and (2)that the resistor divider comprising R8 and R9 replaces resistance R3 ofFIGURE 1. The former difference in the circuit simplifies the wiring ofthe circuit in an actual chassis arrangement, while the latter makes itfeasible readily to derive a signal for use in a musical instrument. Aswill be seen in the chart below, which provides an exemplary set ofvalues for the components of FIGURE 2, the terminal 29 and the bus towhich it and the base electrodes of the transistors T3 and T4 areconnected, is maintained slightly positive relative to a reference valueor ground, so that the signal is devoid of a D.C. component. This isparticularly desirable if the signals are to be applied directlyto thekey switches of an electronic musical instrument. As will be seen in thechart below, the values of R9 and R9 are relatively low (of the order of1000 to 2000 ohms), so that the key switches of the musical instrumentdo not unduly load down the circuit or affect the time constants of thetransistor circuits.

Only a small trigger is required for the operation of circuits inaccordance with my invention. With resistors R6 and R5 of the order of1,000 ohms and 12,000 ohms,

respectively, the actual trigger amplitude equals 1.2 volts,

which is several times the minimum trigger required for the operation ofthe circuit.

The circuits of FIGURES 1 and 2 have been illustrated and described asemploying point-contact transistors. However, it is within the scope ofmy invention to employ other semi-conductive devices, or combinations ofthese, of such type as to provide current gain between a circuit throughthe terminals :1 and c and a circuit between the terminals b and c. Forexample, in FIGURE 3, are illustrated two complementary types ofjunction transistors, connected with the collector electrode of a PNPjunction transistor connected to the base of an NPN junction transistor,the [2 connection being taken from the emitter of the latter transistor.

Another embodiment of a semi-conductor device which may be used in thepractice of my invention is illustrated in FIGURE 4, wherein is shown anNPN junction transistor, the a or emitter-equivalent connection being anelectrode connected to the N-type section of the transistor, as apoint-contact or as a Welded or fused P-type contact. The NPN transistorof this embodiment should be of a relatively low resistivity material.

In FIGURE 5 is illustrated a further embodiment of a semi-conductivedevice suitable for use with the circuits of FIGURES 1 or 2, in the formof a PNPN-type transistor, which is per se Well known in the art, andwherein the a, b and connections are made as shown. This transistor isalso preferably of a relatively low resistivity material.

The embodiment of FIGURE 6 is still another variation of asemi-conductive device suitable for use with my invention, the type ofunit being of the type described to the art by Shockley and sometimescalled the so-called npn I type of semi-conductive device. This devicewould require a DC. source, if employed in the system of FIG- URE I,having opposite polarity.

Following is an exemplary set of values of the components and voltages,of a system in accordance With that illustrated in FIGURE 2:

R5, R 12,000 ohms. R6, R6 1,000 ohms. R7, R7 100 ohms.

R8 17,500 ohms R9 1,350 ohms. R8 21,300 ohms. R9 1,600 ohms. C3 .0082mf.

C4 .015 mf.

T3, T4 s W.E. #1768. E1 Plus .27 volt E2 Minus volts.

Trigger voltage (peak to peak) from master oscillator is 1.05 volts.

be obvious to one skilled in the art that integral division ratiosgreater than 2:1 may be obtained by properselection of components toobtain time constants suitable fo the higher division ratios.

As pointed out above the frequency divider circuit of the presentinvention is particularly adaptable to multiple transistor units on acommon base. The state of the transistor device art has progressed tothe point where a transistor of the type illustrated in FIGURES 8 and 9is feasible. Referring first to FIGURE 8, mounted on a common pedestal30, which may have a suitable electrical connection C comparable to thebase connections of other preceding figures, is a small slab 31, whichmay be of germanium, silicon or other semi-conductor material suitablefor transistor use. In accordance with the teachings of the article byMoll et al. on P-N-P-N transistor switches, in the September 1956Proceedings of the IRE, pages 1174 to 1182, junctions may be arranged asindicated at 32 and 33 to provide P-N-P-N junction transistor units,which may be distributed around the slab 31 as shown in FIGURE 9. Theconductivity types for the various semi-conductor areas of the assemblyare indicated in FIGURE 8. For example if the slab material is N-typethe area 33 is P-type and the area 32 is P-type, and vice versa, asindicated in parentheses. Suitable connections may be made tothe areasshown by leads a'l, b1, and a2, [22, these units being connectable intothe circuits of FIGURES 1 and 2, having corresponding indicia a and b.Interconnecting resistors (not shown), such as R in FIGURE 2, areunderstood to be provided to couple the various divider circuitstogether. If the conductivity types indicated in the drawings Withinparentheses are employed, the polarity of the DC. source must bereversed, as is well understood.

Referring to FIGURE 9, an exemplary arrangement is shown for connectionsto a master oscillator 34, which may be of the type referred tohereinabove. Various divider sections such as 35 and 36 may be connectedas shown, It will be obvious that for 2:1 frequency dividers anarrangement such as that illustrated in FIGURE 9 will furnishharmonically related frequencies f, f/ 2, f/ 4, and so forth.

Although the particular multiple transistor arrangement illustrated inFIGURES 8 and 9 has been above described, it will be obvious that otherand different multiple transistors may be employed. For example,distributed around a common base may be pairs of emitter and collectorpoints contacting the base in the manner conventional for point contacttransistors (not shown). The scope of the arrangement is not,accordingly, restricted to any particular type of transistor systememploying a common base and multiple sets of contacts, but is common toall such arrangements.

While I have described and illustrated one specific embodiment of myinvention, it will be clear that variations of the general arrangementand of the details of construction which are specifically illustratedand described may be restored to without departing from the true spiritand scope of the invention as defined in the appended claim.

What I claim is:

A pulse-repetition-frequency dividing circuit comprising the combinationof a semi-conductive device having first, second and third terminals,said device being capable of providing current gain from a circuitthrough said first and third terminals to a circuit through said secondand third terminals, a pulse input network including two input pointswith a first resistor, a capacitor and a second resistor in series inthat order therebetween, the free end of the second resistor beingconnected to said third terminal, said first terminal being connected tothe common juncture between said second resistor and said capacitor, :1third resistor connected between said second terminal and a secondcommon juncture between said first resistor and said capacitor, a DC.potential source having two terminals, and a fourth resistor having anend connected between said second common juncture and one terminal ofsaid DC. potential source, the other terminal of said D.C. potentialsource being directlyconnected to said third terminal, whereby asub-multiple saw-tooth repetition frequency appears across said secondresistor, and a submultiple frequency of the same frequency as thesawtooth repetition frequency and having sharp pulses of short timeduration relative to the sawtooth duration appear on said secondterminal of said semiconductive device.

References Cited in the file of this patent UNITED STATES PATENTS2,660,624 Bergson Nov. 24, 1953 2,663,800 Herzog Dec. 22, 1953 2,679,594Fromm May 25, 1954 2,731,567 Sziklai et a1. Jan. 17, 1956 2,769,906 Kiddet a1 Nov. 6, 1956 2,797,327 Kidd June 25, 1957 2,826,695 Gray Mar. 11,1958 2,874,311 Turnage Feb. 17, 1959

